1. Field of the Invention
The present invention relates to a distance measuring apparatus for measuring the distance to an object and, more particularly, to a distance measuring apparatus of an active type used in cameras and the like.
2. Related Background Art
An example of the known distance measuring apparatus of the active type used in cameras and the like is a ranging device that has a light detecting unit for detecting light reflected from an object and outputting a near signal and a far signal according to the distance to the object and that is constructed to compare the far signal with a preset clamp signal, calculate an output ratio signal from a ratio of the larger signal resulting from the comparison, and the near signal, and transform the output ratio signal to a distance signal by either of different transformation equations, based on the value of the output ratio signal, as described in Japanese Patent Application Laid-Open No. H10-274524.
This distance measuring apparatus is a ranging device designed to gain a ranging result equivalent to that by the conventional photometry-ranging combination method, without and increase in circuit scale and within a short time and uniquely and stably determining the distance to the object even if it is large.
With this conventional ranging device, however, the ranging accuracy can be degraded if the output ratio signal is integrated multiple times to determine the distance to the object according to the integration result. For example, supposing the output ratio signal is repeatedly integrated multiple times and the far signal is approximately equal to the clamp signal, there will appear a variation in individual output ratio signals to be integrated. In this case, if the output ratio signal is transformed into the distance signal by a transformation equation based on a value of one output ratio signal, it will not be always possible to obtain the proper distance signal according to the distance to the object.
The present invention has been accomplished in order to solve the technical issue as described and an object of the invention is, therefore, to provide a distance measuring apparatus capable of improvement in the ranging accuracy.
In order to achieve the above object, a distance measuring apparatus according to the present invention is an apparatus comprising light projecting means for projecting a beam toward an object to be measured, multiple times; light receiving means for receiving reflected light of each beam projected to the object, at a reception position according to a distance to the object and outputting a far signal, which increases with increase in the distance, and a near signal, which increases with decrease in the distance; clamping means for comparing the far signal with a preset clamp signal, outputting the far signal itself when the far signal is not less than the clamp signal, and outputting the clamp signal when the far signal is smaller than the clamp signal; calculating means for calculating a ratio of the near signal and the output signal from the clamping means and outputting an output ratio signal; output signal detecting means for detecting whether the output signal from the clamping means is the far signal or the clamp signal; integrating means for accumulating the output ratio signal every projection of beam from the light projecting means to perform an integral operation and outputting an integral signal according to the result of the integral operation; and transforming means for transforming the integral signal to a distance signal according to the distance, in accordance with either of different transformation equations selected based on the result of detection of the output signal detecting means.
The distance measuring apparatus according to the present invention is also characterized in that the transforming means transforms the integral signal to the distance signal according to the distance by either of the different transformation equations, based on whether the number of output clamp signals from the clamping means during the integral operation of the integrating means is not less than a set number.
The distance measuring apparatus according to the present invention is also characterized in that the transforming means transforms the integral signal to the distance signal according to the distance by either of the different transformation equations, based on whether the number of output clamp signals from the clamping means during the integral operation of the integrating means is not less than a set number and whether the integral signal is not less than a set value.
According to the present invention, where the integral operation is carried out multiple times in a ranging routine, the integral signal is transformed to the distance signal by either of the different transformation equations, depending upon an output state of the clamp signal in every integral operation. It thus becomes feasible to transform the integral signal to the proper distance signal according to the distance to the object, thereby achieving the improvement in the ranging accuracy.
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present invention.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.